1. Field of the Invention
The present invention relates to crawler appratuses that are mounted on vehicles to replace wheels. More particularly, the present invention pertains to a crawler apparatus that includes a drive wheel, driven wheels, and an endless belt wound about the wheels. Rotation of the belt enables the vehicle to travel stably off-road.
2. Description of the Related Art
Known vehicles provided with crawler apparatuses are adapted to travel over rough terrain, muddy roads, river banks, and terrain covered with snow. Crawler apparatuses replace the normal wheels of the vehicle. Each crawler apparatus has an endless belt that is mounted around a drive wheel and a driven wheel. The drive wheel rotates the belt to move the vehicle. There is a known type of crawler vehicle that has a single crawler apparatus provided on each of its left and right sides. The moving direction of the vehicle is changed by producing a difference between the rotating speed of the left and right crawler apparatuses. However, the rotating speed difference between the belts of each apparatus produces a large resistance which acts on the belts. This makes manuevering the vehicle difficult. Furthermore, in this type of crawler vehicle, each crawler apparatus is assembled integrally with the vehicle and is not designed to be replaced with normal wheels.
A frame of the vehicle supports both the drive wheel and the driven wheel of each crawler apparatus. Therefore, the surface of the terrain, along which the vehicle travels, causes vibrations of the driven wheel. The vibrations are transmitted to the body of the vehicle via the frame and the driven wheels. This makes the ride very uncomfortable.
Japanese Unexamined Utility Model Publication Nos. 60-29777, 62-25286 and Japanese Unexamined Patent Publication No. 3-193573 describe improved crawler apparatuses. Each of the crawler apparatuses is provided with separate frames for the drive wheel and the driven wheel to support each wheel independently. This prevents the vibrations, which are produced when the vehicle is moving, from being transmitted to the body. Elastic members such as rubber and springs are provided between the frames.
Patent Publication No. 3-193573 describes a first type of crawler apparatus that is illustrated in FIG. 20. The apparatus includes a frame 271 that supports a drive wheel (not shown), a frame 273 that supports driven wheels (intermediate rollers) 272, and a rubber block 274 arranged between the frames 271, 273. The rubber block 274 absorbs the vibrations of the driven wheels 272 and prevents the vibrations from being transmitted to the vehicle body. A belt 275 is wound around the drive wheel and the driven wheels 272. The vehicle is moved by rotating the belt 275 with the drive wheel. The frame 273, together with the driven wheels 272, follows the inclination of the belt 275 as it advances along the surface of the terrain. That is, the frame 273 and the wheels 272 incline in correspondence with the inclination of the belt 275. This prevents the belt 275 from falling off from the driven wheels 272.
Utility Model Publication No. 60-29777 describes a second type of crawler apparatus that is illustrated in FIG. 21. The apparatus includes a pair of frames 282, which support a drive wheel (not shown) and extends at the left and right sides of a driven wheel (lower roller) 281, and a rotary shaft 283, which supports the driven wheel 281 so as to enable the wheel 281 to rotate with respect to the frames 282. The shaft 283 is fastened to each frame 282 by bolts 285 with a buffer plate 284 arranged between the frames 282 and the shaft 283. The buffer plate 284 is formed by superimposing sheets of rubber and steel.
Utility Model Publication No. 62-25286 describes a third type of crawler apparatus that includes a pair of frames to rotatably support driven wheels, another frame to support a drive wheel, and a leaf spring located between the frames.
However, in the first type of crawler apparatus shown in FIG. 20, the deforming direction of the rubber block 274 is not restricted. Thus, the inclining direction of the frame 273 is not restricted. This results in shafts 272a of the driven wheels 272 becoming inclined with respect to the axis of the drive wheel. Thus, the driven wheels 272 become inclined with respect to the belt 275. When in such state, the belt 275 may fall off from the driven wheels 272. Furthermore, the rubber block 274 may be damaged due to the torsion force applied thereto.
In the second type of crawler apparatus shown in FIG. 21, the lateral inclination of the driven wheel 281 is restricted by the bolts 285. Thus, the driven wheel 281 does not follow the inclination of the belt. This may result in the belt falling off the wheels 281.
In the third type of crawler apparatus, which is described in Utility Publication No. 62-25286, the lateral inclination of the driven wheels is allowed by the leaf springs arranged at the left and right sides of the same wheels. However, when the driven wheels are inclined, the urging force of the leaf springs differs between the front and rear sides of the driven wheels. This difference may cause a rotary shaft of the driven wheel to become inclined with respect to the axis of the drive wheel and result in the belt falling off the driven wheels.
Japanese Unexamined Patent Publication Nos. 49-19535, 4-8682, and 6-305456 describe a fourth type of crawler apparatus which allows simple maneuvering and facilitates replacement of the apparatus. As shown in FIG. 22, the apparatus includes a triangular crawler 370 which is mounted on the front and rear axles of a vehicle. The crawler 360 includes a drive wheel (sprocket) 371, which is mounted on an axle 360, driven wheels 372, 372, 374, which are arranged below the drive wheel 371, and a belt 376, which is wound about the wheels 371-374 forming a isosceles triangle. The drive wheel 371 transmits power to the belt 376. The driven wheels 372-374 carry the load of the vehicle.
As shown in FIG. 22, in the fourth type of crawler apparatus, the driven wheels 372-374, a plate 375, and the belt 376 pivot freely about the axle 360. The plate 375 supports the wheels 372-374. When the crawler 370 moves over ridges, stones, stumps, or the like, and the inertial force of the vehicle is great, the crawler 370 may pivot about the front driven wheel 372, as shown by the broken lines in FIG. 22, if the wheel 372 collides against obstacles. This is due to the downward forces W1, W2 acting equally from the front and rear driven wheels 372, 373 and the inertial force F acting on the axis of the drive wheel 371. The large inertial force F produces moment in the crawler 370.
To prevent the crawler 370 from pivoting out of a certain range, a stopper 377 may be provided, as shown in FIG. 22. The stopper 377 is fixed to body of the vehicle and arranged encompassing the axle 360 with two arms 377a, 377b extending from the axle 360. A protrusion 378 is provided on the plate 375. As the crawler 370 including the plate 377 is pivoted about the axle 360, the protrusion 378 is abutted against the arms 377a, 377b. This restricts the pivoting of the crawler 370. When in contact with the arms 377a, 377b, the load applied to the protrusion 378 is relatively large. The load may inflict damage on the protrusion 378. Furthermore, the stopper 375 is required to be provided on the plate 377 so that the stopper 375 moves integrally with the crawler 370. This restricts the location of the stopper 375
A fifth type of a crawler apparatus is shown in FIGS. 23 and 24. As shown in FIG. 23, a triangular crawler 481 includes a drive wheel 482, pairs of axially aligned driven wheels 483, 484, pairs of axially aligned intermediate driven wheels 485, 486 arranged between the driven wheels 483, 484, and a belt 487 wound about the wheels 482-486. The belt 487 has a plurality of projections 487a arranged along its inner surface. A groove 482a is defined along the circumferential surface of the drive wheel 482. A plurality of pins 489 extend across the groove 482a. The pins 489 of the drive wheel 482 engage with the projections 487a of the belt 487 to transmit the power of the drive wheel 482 to the belt 487.
As shown in FIG. 24, each pair of driven wheels 483-486 is arranged with one wheel on the left side of the projections 487a and the right wheel on the other side. The projections 487a are guided into the space defined between each pair of wheels 483-486 and prevent the belt 487 from falling off from the wheels 483-486. The drive wheel 482 includes rims 482b on each of its sides. The rims 482b define the groove 482a. The rims 482b support and apply sufficient tension to the belt 487. The groove 482a of the drive wheel 482 receives the projections 487a of the belt 487 to prevent the belt 487 from falling off. A bracket 488a of a frame 488 is arranged between each pair of intermediate driven wheels 485, 486 to support the wheels 485, 486.
The triangular shape of the crawler 481 increases the contact space between the crawler 481 and the surface of the terrain. This ensures the traction of the crawler 481. However, the crawler 481 may be pivoted about the axis of the drive wheel 482 when it collides against obstacles as the vehicle advances. This may result in displacement of the crawler 481. To cope with this, a pivot prevention stopper may be provided in the vehicle.
It is preferable that triangular crawlers be flattened to lower their center of gravity. This suppresses the pivoting of the crawler when it collides against obstacles. To flatten the crawler, the diameter of the drive wheel and the driven wheels (particularly, the intermediate driven wheels) may be reduced. However, the ratio of the engine speed with respect to the vehicle velocity is substantially proportional to the diameter of the drive wheel. Therefore, reducing the diameter of the drive wheel to flatten the crawler results in a decrease in the maximum speed of the vehicle. Accordingly, it is required that the engine of a vehicle that employs triangular crawlers be driven at a higher speed than that of a vehicle that employs ordinary wheels to obtain the same vehicle velocity. This increases fuel consumption. If the diameter of the intermediate driven wheels is minimized, the engaging ratio of the belt with respect to each wheel decreases. This tends to result in the belt falling off the driven wheels.
To solve these problems, the drive wheel may be arranged near the driven wheels. Japanese Unexamined Patent Publication No. 4-8682 describes a triangular crawler having a drive wheel and driven wheels that are overlapped with one another. This structure flattens the crawler without reducing the diameter of the drive and driven wheels. Holes are provided throughout the belt so as to enable the drive wheel to become engaged with the holes. A small space is provided between the pair of axially aligned intermediate driven wheels. The drive wheel, the width of which corresponds to the space, is inserted into the space. This structure prevents the belt from falling off from the drive wheel.
However, the fifth type of crawler apparatus illustrated in FIGS. 23 and 24 employs a structure in which the drive wheel 482 engages the projections 487a of the belt 487. Thus, the thickness of the rims 482b become insufficient when reducing the thickness of the drive wheel 482. Accordingly, this structure hinders the smooth guiding of the projections 487a of the belt 487 into the driven wheel 482 and results in the belt 487 tending to fall off from the drive wheel 482. Therefore, although the structure described in Patent Publication No. 4-8682 flattens the crawler without reducing the diameter of the wheels, this structure necessitates steel cores to be embedded in the belt to increase its strength. This increases the number of steps required to manufacture the belt. Furthermore, as the vehicle advances, the impact between the steel cores and the ground surface increases the noise and vibrations produced by the belt.